This invention relates to a fixing apparatus which has a heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material.
At present, a fixing apparatus of the heat roller type which is used in an image forming apparatus such as a copying machine and a laser beam printer is composed of a heating roller having a halogen heater lamp as a heat source inside and being provided with a coating layer for a better releasing ability, and a pressing roller having a surface layer made of a rubber material.
Incidentally, in an image forming apparatus having a fixing apparatus of the above-described structure, two thirds of the electric power is consumed in the fixing apparatus during image formation.
Further, in order to make it possible to form an image whenever it is required, the heating roller of the fixing apparatus is always kept at a predetermined temperature even in standby hours, and two thirds of the electric power of the standby hours also is consumed in the fixing apparatus.
Incidentally, the electric power consumption of a fixing apparatus during the formation of an image is approximately determined by the product of the heat quantity which is necessary for fixing a sheet of transfer material times the number of sheets having an image formed.
In an image forming apparatus of a class with an image forming speed of 20-30 sheets per minute, the heat quantity required for a unit time is small in proportion to the slow speed of image forming, and it is not necessary to store heat in the heating roller; thus, sufficient heat can be supplied at the time of image forming.
Accordingly, from the point of view to save energy, it has been proposed a heating roller having its heat capacity made small by making the thickness of its metallic sleeve as thin as possible.
However, if a heating roller with a thin sleeve is used, there are problems as follows:.
(1) Because the heat capacity of the heating roller is small, the difference between the required heat quantity during fixing and that in idling hours is large.
Accordingly, in the case where a control, in which the supply of electric current to the heating means is turned on and off at a set temperature, is carried out for the temperature control of the heating roller, when fixing is finished and the driving for the rotation of the heating roller is stopped, if the heating means is still actuated, the heat quantity immediately after the stop becomes excessive because of the large supplied heat quantity before and after the stop of rotation of the heating roller; hence, the temperature of the heating roller becomes abnormally higher than the set temperature owing to the overshoot, which results in a useless consumption of electric power.
(2) In the case where a large number of sheets of transfer material having a small width are continuously fixed, only a part of the heating roller (for example, only the central portion of the heating roller) requires heat.
Especially, in the case where plural sheets of transfer material, like sheets of 5.5xc3x978.5R, having a proportion of the smallest width and a larger length in the flow direction than the sheets of transfer material of A-sizes and B-sizes are continuously fixed, there is also a problem that it occurs that unnecessary area is heated, and the temperature rise of the portion with which no paper sheet comes in contact becomes remarkable in accordance with the small heat capacity of the heating roller, which makes the temperature control difficult.
(3) In the case where a control, in which the supply of electric current to the heating means is turned on and off at a set temperature, is carried out for the temperature control of the heating roller, because the heat capacity of the heating roller is small, the temperature of the heating roller rises and drops with respect to the set temperature, and the frequency of turning on and off of the current supply becomes high.
There is also a problem that, when the heating means is turned on, a noise is produced owing to a rush current.
Heretofore, it has been known that, in order to suppress the electric power consumption of a fixing apparatus, the sleeve of its heating roller is made thin, as is disclosed in the publications of Tokkaihei H7-64420 and Tokkaihei H9-297486. However, in order to obtain a good fixing result through using a thin-sleeve roller, it is necessary to use an optimum fixing condition which is suitable to it, and if a fixing condition which is the same as that used for a conventional thick-sleeve roller was used, a good fixing result could not be obtained. Therefore, it is an object of this invention to provide a fixing apparatus which gives a good fixing result while suppressing electric power consumption by using a thin-sleeve roller.
It is the second object of the invention to provide a fixing apparatus which eliminates a useless electric power consumption at the time of completion of fixing.
It is the third object of the invention to provide a fixing apparatus which is capable of making a temperature control with a high precision in the case where plural sheets of transfer material having a small width are continuously fixed.
It is the fourth object of the invention to provide a fixing apparatus which reduces the generation of noise.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by a fixing apparatus and an image forming apparatus described as follow.
(1) A fixing apparatus for fixing a toner image onto a transfer material, comprising a heating roller being a hollow cylinder, thickness of which is less than 2.0 mm, made of either aluminum or iron, a heat source positioned interior of the heating roller, a pressing roller, comprised of a silicone rubber having a surface hardness ranging from 35xc2x0 to 75xc2x0 (Asker C hardness), being in pressure contact with the heating roller to form a nip between the heating roller and the pressing roller, wherein a nip pressure at the nip is in a range of 0.2-2.0 kgf/cm2, and a controller to control a conveyance velocity of the transfer material, so that the transfer material passes through the nip within a nip passing time ranging from 20 msec to 40 msec.
(2) An image forming apparatus, comprising an image bearing element to form a latent image on it, a developing device to form a toner image on the image bearing element, a transferring device to transfer the toner image, formed by the developing device, onto a transfer material a fixing device to fix the toner image, transferred by the transferring device, onto the transfer material, the fixing device comprising, a heating roller being a hollow cylinder made of either aluminum or iron, thickness of which is less than 2.0 mm, a heat source positioned interior of the heating roller, and a pressing roller, comprised of a silicone rubber having a surface hardness ranging from 35xc2x0 to 75xc2x0 (Asker C hardness), being in pressure contact with the heating roller to form a nip between the heating roller and the pressing roller, wherein a nip pressure at the nip is in a range of 0.2-2.0 kgf/cm2, and a controller to control a conveyance velocity of the transfer material, so that the transfer material passes through the nip within a nip passing time ranging from 20 msec to 40 msec.
Further, to overcome the abovementioned problems, other fixing apparatuses, embodied in the present invention, will be described as follows:
(3) A fixing apparatus which has a heating roller having a heat source inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein said heating roller has a cylindrical sleeve made of either aluminum or iron and a thickness equal to or smaller than 2.0 mm, said pressing roller is made of a silicone rubber and has a surface hardness (Asker C hardness) of 35-75, the nip pressure between said heating roller and said pressing roller is 0.2-2.0 kgf/cm2, and the passing time through the nip is 20-40 msec.
The electric power consumption of a fixing apparatus during the formation of an image is approximately determined by the product of the heat quantity which is necessary for fixing a sheet of transfer material times the number of sheets having an image formed.
In an image forming apparatus of a class with an image forming speed of 20-30 sheets per minute, the heat quantity required for a unit time is small in proportion to the slow speed of image forming, and it is not necessary to store heat in the heating roller; thus, sufficient heat can be supplied at the time of image forming.
Accordingly, it is desirable to make the sleeve of a heating roller as thin as possible.
By making the material of the sleeve of the heating roller either aluminum or iron and the thickness of the sleeve equal to or smaller than 2.0 mm, that is, by making it thin, the heat capacity of the heating roller is made small, which makes the thermal efficiency high.
Further, by making the material of the pressing roller a silicone rubber, its surface hardness (Asker C hardness) 35-75, the nip pressure between said heating roller and said pressing roller 0.2-2.0 kgf/cm2, and the nip passing time 20-40 msec, that is, by making the pressing roller of a soft material, the nip time of a transfer material is made long, and the heat quantity to be supplied to the transfer material can be secured.
Besides, according to the result of experiments by the inventors of this application, it is confirmed that the thickness of the sleeve should desirably be 0.6-2.0 mm if the sleeve is made of aluminum, and 0.3-1.0 mm for iron.
(4) A fixing apparatus set forth in the above-described paragraph (2), wherein a first heating means for heating the area which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of a predetermined size passes, and a second heating means for heating the area which a sheet of transfer material of the predetermined size passes are provided in the aforesaid heating roller.
By providing a first heating means for heating the area which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of a predetermined size passes, and a second heating means for heating the area which a sheet of transfer material of the predetermined size passes, and independently controlling for driving the first heating means and the second heating means, even in the case where a sheet of transfer material having a size equal to or smaller than a predetermined size is fixed, it can be prevented the temperature rise of the portion which no sheet of paper comes in contact with and is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of the predetermined size passes; thus, the useless area is not heated and the electric power consumption of the heating means is reduced.
(5) A fixing apparatus set forth in the above-described paragraph (4), wherein the heat distribution ratio in the aforesaid first heating means are equal to or larger than 15% for the area which a sheet of transfer material of the predetermined size passes on condition that it is 100% for the area outside the area which a sheet of transfer material of the predetermined size passes.
By making such a heat distribution ratio, by turning the first heating means on and off during idling, even if the second heating means is in the off-state, the temperature over the whole area of the heating roller can be kept approximately uniform.
Thus, the number of times of turning on and off of the heating means can be reduced, and the generation of a noise can be prevented.
(6) A fixing apparatus set forth in the above-described paragraph (4) or (5), wherein the heat distribution ratio in the aforesaid second heating means is equal to or smaller than 60% for the area outside the area which a sheet of transfer material of the predetermined size passes on condition that it is 100% for the area which a sheet of transfer material of the predetermined size passes.
By making such a heat distribution ratio, even when plural sheets of transfer material having a width smaller than the predetermined size are continuously fixed, the temperature of the heating roller can be kept at a predetermined temperature by only the second heating means.
(7) A fixing apparatus set forth in any one of the above-described paragraphs (4) to (6), wherein a first temperature detecting means for detecting the temperature of the area of the aforesaid heating roller which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of the predetermined size passes, and a second temperature detecting means for detecting the temperature of the area of the said heating roller which a sheet of transfer material of the predetermined size passes are provided.
By providing a first temperature detecting means for detecting the temperature of the area of the aforesaid heating roller which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of the predetermined size passes, and a second temperature detecting means for detecting the temperature of the area of said heating roller which a sheet of transfer material of the predetermined size passes, a precise temperature control for the first heating means and the second heating means can be done, and the electric power consumption is reduced.
(8) A fixing apparatus set forth in any one of the above-described paragraphs (4) to (7), wherein a thermostat is provided in the neighborhood of the border of the aforesaid first heating means and the aforesaid second heating means of the heating roller.
In the case where the formation of an image is continuously carried out on a large number of sheets of transfer material having a width smaller than the predetermined size, the temperatures of the both side portions in the first heating means rise extremely; however, by providing a thermostat in the neighborhood of the border of the aforesaid first heating means and the aforesaid second heating means of the heating roller, it can be prevented that the heating roller reaches a temperature higher than the set temperature by cutting the supply of the electric power to the first heating means by the thermostat, and further, the electric power consumption is reduced.
(9) A fixing apparatus set forth in any one of the above-described paragraphs (5) to (7), wherein it is provided a cooling means for cooling the both side portions of the area of the heating roller which a sheet of transfer material of the predetermined size passes.
By providing a cooling means for cooling the both side portions of the area of the heating roller which a sheet of transfer material of the predetermined size passes, in the case where the formation of an image is carried out on sheets of transfer material having a width smaller than the predetermined size, when the temperatures of the both side portions in the second heating means rise extremely, it can be prevented by cooling the heating roller by the cooling means that the heating roller reaches a temperature higher than the set temperature.
(10) A fixing apparatus set forth in any one of the above-described paragraphs (3) to (8), wherein it is provided a cleaning mechanism having a web which is in contact with the aforesaid heating roller.
Because only the web having a small heat capacity of the cleaning mechanism is contact with the heating roller, the electric power consumption is small.
(11) A fixing apparatus which has a heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein said heating roller has a cylindrical sleeve made of either aluminum or iron and a thickness equal to or smaller than 2.0 mm, and a first heating means for heating the area which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of a predetermined size passes, and a second heating means for heating the area which a sheet of transfer material of the predetermined size passes are provided in the aforesaid heating roller.
The electric power consumption of a fixing apparatus during the formation of an image is approximately determined by the product of the heat quantity which is necessary for fixing a sheet of transfer material times the number of sheets having an image formed.
In an image forming apparatus of a class with an image forming speed of 20-30 sheets per minute, the heat quantity required for a unit time is small in proportion to the slow speed of image forming, and it is not necessary to store heat in the heating roller; thus, sufficient heat can be supplied at the time of image forming.
Accordingly, it is desirable to make the sleeve of a heating roller as thin as possible.
By making the material of the sleeve of the heating roller either aluminum or iron and the thickness of the sleeve equal to or smaller than 2.0 mm, that is, by making it thin, the heat capacity of the heating roller is made small, which makes the thermal efficiency high.
By providing a first heating means for heating the area which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of a predetermined size passes, and a second heating means for heating the area which a sheet of transfer material of the predetermined size passes, and independently controlling for driving the first heating means and the second heating means, even in the case where a sheet of transfer material having a size equal to or smaller than a predetermined size is fixed, it can be prevented the temperature rise of the portion which no sheet of paper comes in contact with and is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of the predetermined size passes; thus, the useless area is not heated and the electric power consumption of the heating means is reduced.
(12) A fixing apparatus set forth in the above-described paragraph (11), wherein the heat distribution ratio in the aforesaid first heating means are equal to or larger than 15% for the area which a sheet of transfer material of the predetermined size passes on condition that it is 100% for the area outside the area which a sheet of transfer material of the predetermined size passes.
By making such a heat distribution ratio, by turning the first heating means on and off during idling, even if the second heating means is in the off-state, the temperature over the whole area of the heating roller can be kept approximately uniform.
Thus, the number of times of turning on and off of the heating means can be reduced, and the generation of a noise can be prevented.
(13) A fixing apparatus set forth in the above-described paragraph (11) or (12), wherein the heat distribution ratio in the aforesaid second heating means is equal to or smaller than 60% for the area outside the area which a sheet of transfer material of the predetermined size passes on condition that it is 100% for the area which a sheet of transfer material of the predetermined size passes.
By making such a heat distribution ratio, even when plural sheets of transfer material having a width smaller than the predetermined size are continuously fixed, the temperature of the heating roller can be kept at a predetermined temperature by only the second heating means.
(14) A fixing apparatus which has a heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein a control section is provided for forcibly stopping the driving of said heating means for a time, when fixing is completed and the driving for the rotation of said heating roller is stopped, and then, controls driving of said heating means during an idling state of said fixing apparatus.
Useless consumption of the electric power is eliminated by stopping the driving of the aforesaid heating means by the control section when fixing is completed and the driving for the rotation of said heating roller is stopped, since the overshoot of temperature of the heating roller can be suppressed.
(15) A fixing apparatus which has a heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein a first heating means provided in said heating roller for heating the area which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of transfer material of a predetermined size passes, a second heating means provided in said heating roller for heating the area which a sheet of transfer material of the predetermined size passes are provided in the aforesaid heating roller, a first temperature detecting means for detecting the temperature of the area of said heating roller which is inside the area which a sheet of transfer material of the maximum size passes and is outside the area which a sheet of the predetermined size passes, and a second temperature detecting means for detecting the temperature of the area of said heating roller which a sheet of transfer material of the predetermined size passes, a cooling means for cooling the area of said heating roller which is outside the area which a sheet of transfer material of the predetermined size passes, and a control section for driving said cooling means in the case where a sheet of transfer material having a width smaller than the predetermined size is fixed, while lowering the set temperature of said first heating means and lowering the set temperature of said second heating means after a predetermined number of copies are provided.
In the case where sheets of transfer material having a width smaller than the predetermined size are fixed, by the control section driving the aforesaid cooling means while lowering the set temperature of said second heating means after a predetermined number of copies, it is made high the precision of the temperature control when sheets of transfer material having a narrow width are fixed.
(16) A fixing apparatus which has a thin-sleeve heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein a temperature detecting means for detecting the temperature of said heating roller and a control section which, during idling, stops said heating means when said heating roller reaches a temperature equal to or higher than a first set temperature, and drives said heating means when said heating roller has a temperature equal to or lower than a second set temperature which is lower than said first set temperature are provided.
During idling, by the control section stopping said heating means when said heating roller reaches a temperature equal to or higher than a first set temperature, and driving said heating means when said heating roller has a temperature equal to or lower than a second set temperature which is lower than said first set temperature, that is, by making a control having a hysteresis, the frequency of turning on and off of the heating means is reduced, and the generation of a noise is suppressed.